Winding switching apparatus and winding switching system

ABSTRACT

A winding switching apparatus includes a winding switching device and a drive circuit. The winding switching device is configured to switch a plurality of windings of an AC motor. The drive circuit is configured to control the winding switching device. The winding switching device includes a winding switch, a diode bridge, and a capacitor. The diode bridge includes a positive-side DC output terminal, a negative-side DC output terminal, and AC input terminals. The AC input terminals corresponds to respective phases of the AC motor. The positive-side and negative-side DC output terminals are respectively connected to positive-side and negative-side DC buses provided in an inverter. The AC input terminals are respectively connected to winding-switching terminals corresponding to the respective phases of the AC motor. The AC input terminals are respectively connected to phase terminals provided in the winding switch.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of the U.S. patentapplication Ser. No. 12/789,385 filed May 27, 2010, which in turn is acontinuation application of PCT/JP2008/071660, filed Nov. 28, 2008,which claims priority to Japanese Patent Application No. 2007-336294,filed Dec. 27, 2007. The contents of these applications are incorporatedherein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a winding switching apparatus and awinding switching system.

2. Discussion of the Invention

For driving devices for main shafts of machine tools and vehicles whichare driven by inverter apparatuses, winding switching methods have beenadopted to produce a sufficiently large torque in a low-speed range andallow operation in a high-speed range.

For example, U.S. Pat. No. 6,847,185 B2 (family member: JapaneseUnexamined Patent Application Publication No. 2003-111492) describes awinding switching apparatus that includes an AC motor having externalterminals for switching windings, an inverter unit configured to supplya variable voltage having a variable frequency to the AC motor, and awinding switching unit having semiconductor switches.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a winding switchingapparatus includes a winding switching device and a drive circuit. Thewinding switching device is configured to switch a plurality of windingsof an AC motor which is configured to be driven by an inverter to supplya variable voltage having a variable frequency. The drive circuit isconfigured to control the winding switching device. The windingswitching device includes a winding switch, a diode bridge, and acapacitor. The winding switch is configured to switch the plurality ofwindings based on a winding-switching signal from the drive circuit. Thediode bridge includes a positive-side DC output terminal, anegative-side DC output terminal, and AC input terminals. The AC inputterminals corresponds to respective phases of the AC motor. Thepositive-side and negative-side DC output terminals are respectivelyconnected to positive-side and negative-side DC buses provided in theinverter. The AC input terminals are respectively connected towinding-switching terminals corresponding to the respective phases ofthe AC motor. The AC input terminals are respectively connected to phaseterminals provided in the winding switch. The capacitor connects thepositive-side DC output terminal to the negative-side DC outputterminal.

According to another aspect of the present invention, a windingswitching system includes an AC motor, an inverter, a winding switchingdevice, and a drive circuit. The inverter is to supply a variablevoltage having a variable frequency. The winding switching device isconfigured to switch a plurality of windings of the AC motor which isconfigured to be driven by the inverter. The drive circuit is configuredto control the winding switching device. The winding switching deviceincludes a winding switch, a diode bridge, and a capacitor. The windingswitch is configured to switch the plurality of windings based on awinding-switching signal from the drive circuit. The diode bridgeincludes a positive-side DC output terminal, a negative-side DC outputterminal, and AC input terminals. The AC input terminals corresponds torespective phases of the AC motor. The positive-side and negative-sideDC output terminals are respectively connected to positive-side andnegative-side DC buses provided in the inverter. The AC input terminalsare respectively connected to winding-switching terminals correspondingto the respective phases of the AC motor. The AC input terminals arerespectively connected to phase terminals provided in the windingswitch. The capacitor connects the positive-side DC output terminal tothe negative-side DC output terminal.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a diagram illustrating a winding switching apparatus forswitching windings of an AC three-phase motor according to a firstembodiment of the present invention;

FIG. 2A and FIG. 2B are graphs showing operation waveforms (simulationwaveforms) of a winding switching operation performed by the windingswitching apparatus according to the first embodiment of the presentinvention;

FIG. 3 is a diagram illustrating a winding switching apparatus forswitching windings of an AC three-phase motor according to a secondembodiment of the present invention; and

FIG. 4 is a diagram illustrating detailed circuit configurations of astate detector and a comparator included in the winding switchingapparatus according to the second embodiment of the present invention.

DESCRIPTION OF THE EMBODIMENTS

Embodiments will now be described with reference to the accompanyingdrawings, wherein like reference numerals designate corresponding oridentical elements throughout the various drawings. The description ofsuch elements will not be repeated.

Although an actual inverter has many functions and components, onlythose related to embodiments of the present invention are illustrated inthe drawings and will be described.

FIG. 1 is a diagram illustrating a winding switching apparatus forswitching windings of an AC three-phase motor according to a firstembodiment of the present invention. Referring to FIG. 1, referencenumeral 1 denotes an AC three-phase motor, reference numerals 2 and 11denote winding switching sections, reference numerals 3 and 12 denotediode units, reference numerals 4 and 13 denote switching units,reference numerals 5 and 14 denote positive-side charging resistors,reference numerals 6 and 15 denote capacitors, reference numeral 7denotes an inverter, reference numerals 8 and 16 denote drive circuits,reference numeral 9 denotes a positive-side direct current (DC) bus,reference numeral 10 denotes a negative-side DC bus, reference numerals17 and 18 denote drive signals, reference numerals 19 and 20 denoteprotective diode units, reference numerals 21 and 22 denotenegative-side charging resistors, and reference numeral 23 and 24 denotepotential fixing units.

The inverter 7 includes a control unit and a main circuit unit. The ACthree-phase motor 1 has windings for the respective three phases.Intermediate taps (TU2, TV2, and TW2), winding start terminals (TU1,TV1, and TW1), and winding end terminals (TU3, TV3, and TW3) of therespective windings are provided outside the AC three-phase motor 1.

The winding start terminals (TU1, TV1, and TW1) are connected to theinverter 7, the winding end terminals (TU3, TV3, and TW3) are connectedto the winding switching section 11, and the intermediate taps (TU2,TV2, and TW2) are connected to the winding switching section 2.

The drive circuit 8 receives the drive signal 17 from the control unitof the inverter 7, drives the winding switching section 2, and outputs acontrol signal to the switching unit 4. Similarly, the drive circuit 16receives the drive signal 18 from the control unit of the inverter 7,drives the winding switching section 11, and outputs a control signal tothe switching unit 13.

First, the winding switching section 2 will be described. The windingswitching section 2 includes the diode unit 3, the switching unit 4, thepotential fixing unit 23, and the protective diode unit 19.

The diode unit 3 includes three diodes whose cathodes are connected toeach other.

The switching unit 4 includes three power semiconductor switches andthree diodes connected in inverse parallel to the respective powersemiconductor switches. The collectors of the power semiconductorswitches are connected to the respective anodes of the diodes of thediode unit 3, while the emitters of the power semiconductor switches areconnected to each other.

Connection points between the respective anodes of the diodes of thediode unit 3 and the corresponding collectors of the power semiconductorswitches of the switching unit 4 are connected to the respectiveintermediate taps (TU2, TV2, and TW2).

The potential fixing unit 23 includes the positive-side chargingresistor 5, the capacitor 6, and the negative-side charging resistor 21.One end of the positive-side charging resistor 5 is connected to thepositive-side DC bus 9 of the inverter 7, and the other end of thepositive-side charging resistor 5 is connected to the positive side ofthe capacitor 6. The negative side of the capacitor 6 is connected toone end of the negative-side charging resistor 21, and the other end ofthe negative-side charging resistor 21 is connected to the negative-sideDC bus 10. A connection point between the positive side of the capacitor6 and the positive-side charging resistor 5 is connected to the cathodesof the diode unit 3.

The protective diode unit 19 includes three diodes whose anodes areconnected to the negative side of the capacitor 6 and whose cathodes areconnected to the respective intermediate taps (TU2, TV2, and TW2).

Although insulated gate bipolar transistors (IGBTs) are used here as thepower semiconductor switches of the switching unit 4, any powersemiconductor switches suitable for the voltage and current may be used.

The winding switching section 11 has the same configuration as that ofthe winding switching section 2. The winding switching section 11includes the diode unit 12, the switching unit 13, the potential fixingunit 24, and the protective diode unit 20.

The diode unit 12 includes three diodes whose cathodes are connected toeach other.

The switching unit 13 includes three power semiconductor switches andthree diodes connected in inverse parallel to the respective powersemiconductor switches. The collectors of the power semiconductorswitches are connected to the respective anodes of the diodes of thediode unit 12, S01 while the emitters of the power semiconductorswitches are connected to each other.

Connection points between the respective anodes of the diodes of thediode unit 12 and the corresponding collectors of the powersemiconductor switches of the switching unit 13 are connected to therespective winding end terminals (TU3, TV3, and TW3).

The potential fixing unit 24 includes the positive-side chargingresistor 14, the capacitor 15, and the negative-side charging resistor22. One end of the positive-side charging resistor 14 is connected tothe positive-side DC bus 9 of the inverter 7, and the other end of thepositive-side charging resistor 14 is connected to the positive side ofthe capacitor 15. The negative side of the capacitor 15 is connected toone end of the negative-side charging resistor 22, and the other end ofthe negative-side charging resistor 22 is connected to the negative-sideDC bus 10. A connection point between the positive side of the capacitor15 and the positive-side charging resistor 14 is connected to thecathodes of the diode unit 12.

The protective diode unit 20 includes three diodes whose anodes areconnected to the negative side of the capacitor 15 and whose cathodesare connected to the respective winding end terminals (TU3, TV3, andTW3).

Although IGBTs are used here as the power semiconductor switches of theswitching unit 13, any power semiconductor switches suitable for thevoltage and current may be used.

When the switching unit 4 is turned on, an ON signal is output to allthe power semiconductor switches of the switching unit 4. This allowscurrent to flow through one or more power semiconductor switches towhich a forward voltage is applied. Although no current flows throughthe other one or more power semiconductor switches to which a reversevoltage is applied, current flows through the corresponding one or morediodes connected in inverse parallel to the other one or more powersemiconductor switches. Thus, the intermediate taps (TU2, TV2, and TW2)are shorted to each other.

When the switching unit 4 is turned off, an OFF signal is output to allthe power semiconductor switches of the switching unit 4. This turns offall the power semiconductor switches of the switching unit 4, so thatthe intermediate taps (TU2, TV2, and TW2) are opened.

When the switching unit 13 is turned on, an ON signal is output to allthe power semiconductor switches of the switching unit 13. This allowscurrent to flow through one or more power semiconductor switches towhich a forward voltage is applied. Although no current flows throughthe other one or more power semiconductor switches to which a reversevoltage is applied, current flows through the corresponding one or morediodes connected in inverse parallel to the other one or more powersemiconductor switches. Thus, the winding end terminals (TU3, TV3, andTW3) are shorted to each other.

When the switching unit 13 is turned off, an OFF signal is output to allthe power semiconductor switches of the switching unit 13. This turnsoff all the power semiconductor switches of the switching unit 13, sothat the winding end terminals (TU3, TV3, and TW3) are opened.

Next, a high-speed operation of the AC three-phase motor 1 will bedescribed. For the high-speed operation, the switching unit 4 is turnedon and the switching unit 13 is turned off. This causes, through theswitching unit 4, the intermediate taps (TU2, TV2, and TW2) to shorteach other to form a star connection composed of TU1-TU2, TV1-TV2, andTW1-TW2. Thus, as compared to the case where the winding end terminals(TU3, TV3, and TW3) are shorted, the number of winding segments can bereduced and a counter-electromotive force of the AC three-phase motor 1can be suppressed. This allows a sufficient amount of current to flowand allows the AC three-phase motor 1 to operate at high speed.

For a low-speed operation of the AC three-phase motor 1, the switchingunit 13 is turned on and the switching unit 4 is turned off. Thiscauses, through the switching unit 13, the winding end terminals (TU3,TV3, and TW3) to short each other to form a star connection composed ofTU1-TU3, TV1-TV3, and TW1-TW3. Thus, a sufficient torque can be producedby low-speed operation of the AC three-phase motor 1.

As described above, a wide range of output characteristics (i.e., a widerange of speed/torque control) can be achieved by controlling theswitching unit 4 and the switching unit 13 depending on the speed ofoperation.

In the known winding switching methods described above, energy stored inmotor inductance is released during transition of motor windings from anexcited state to a non-excited state. This interferes with instantaneousswitching of current and causes fluctuations in motor current. In thepresent invention, however, a charged capacitor is present in a windingswitching section. This allows instantaneous switching of current, sothat the motor current waveform of the switching operation is smoothed.

A description will now be given of why the presence of a chargedcapacitor in a winding switching section allows instantaneous switchingof current.

At the time of winding switching, the amount of current remaining inmotor windings can be rapidly reduced to zero by increasing the currentreduction rate. A current reduction rate di/dt defined by temporaldifferentiation of current is expressed by Equation 1 below:

di/dt=V/L   Equation 1

where V is a capacitor voltage and L is a motor winding inductance.Maintaining the capacitor voltage V at a high potential makes itpossible to increase the current reduction rate and to rapidly reducethe amount of current to zero.

An operation for transition from low-speed windings to high-speedwindings will now be described.

For transition from low-speed windings to high-speed windings, theswitching unit 4 is turned on and the switching unit 13 is turned off.The capacitor 15 that is connected, through the positive-side chargingresistor 14 and the negative-side charging resistor 22, between thepositive-side DC bus 9 and the negative-side DC bus 10 of the inverter 7is subjected to initial charging in advance. Then, when switching ofmotor windings is made, that is, when the switching unit 13 is turnedoff, energy stored in the motor inductance is absorbed through the diodeunit 12 by the capacitor 15. Although this increases the voltage of thecapacitor 15 to a level higher than the initial charging voltage (DC busvoltage), the current flowing through the motor windings is rapidlyreduced to zero.

FIG. 2A and FIG. 2B are graphs showing operation waveforms (simulationwaveforms) of a winding switching operation performed by the windingswitching apparatus of the present embodiment. FIG. 2A shows capacitorvoltage waveforms, and FIG. 2B shows waveforms of current flowingthrough motor windings. Referring to FIG. 2A, “A” indicates a capacitorvoltage waveform for the present embodiment where an initial chargingvoltage is 350 V, and “B” indicates a capacitor voltage waveform for aknown method where no initial charging is performed. Referring to FIG.2B, “C” indicates a waveform of current flowing through motor windingsin the present embodiment where an initial charging voltage is 350 V,and “C” indicates a waveform of current flowing through motor windingsin the known method where no initial charging is performed.

When the initial charging voltage of the capacitor is 350 V, the currentreduction rate is higher and the current is more rapidly reduced tozero, as compared to the case where the initial charging voltage of thecapacitor is 0 V. This shows that depending on whether the capacitor hasbeen subjected to initial charging, the length of time before thecurrent flowing through motor windings is reduced to zero is different.

When the switching unit 4 is in an OFF state, no motor current flowsthrough the winding switching section 2. When the switching unit 4 isturned on, a common connection point of the power semiconductor switchesof the switching unit 4 becomes a motor neutral point. Thus, motorcurrent flows through the windings TU1-TU2, TV1-TV2, and TW1-TW2 of theAC three-phase motor 1, the power semiconductor switches of theswitching unit 4, and the diodes connected in inverse parallel to thesepower semiconductor switches.

The same principle applies to the case of transition from high-speedwindings to low-speed windings. An operation for transition fromhigh-speed windings to low-speed windings will now be described.

For transition from high-speed windings to low-speed windings, theswitching unit 13 is turned on and the switching unit 4 is turned off.The capacitor 6 that is connected, through the positive-side chargingresistor 5 and the negative-side charging resistor 21, between thepositive-side DC bus 9 and the negative-side DC bus 10 of the inverter 7is subjected to initial charging in advance. Then, when switching ofmotor windings is made, that is, when the switching unit 4 is turnedoff, energy stored in the motor inductance is absorbed through the diodeunit 3 by the capacitor 6. Although this increases the voltage of thecapacitor 6 to a level higher than the initial charging voltage (DC busvoltage), the current flowing through the motor windings is rapidlyreduced to zero.

When the switching unit 13 is turned on, a common connection point ofthe power semiconductor switches of the switching unit 13 becomes amotor neutral point. Thus, motor current flows through the windingsTU1-TU3, TV1-TV3, and TW1-TW3 of the AC three-phase motor 1, the powersemiconductor switches of the switching unit 13, and the diodesconnected in inverse parallel to these power semiconductor switches.

With the configuration described above, it is possible to provide thewinding switching apparatus capable of quickly switching windings of theAC three-phase motor.

Next, an operation of the protective diode units 19 and 20 will bedescribed. If an abnormality occurs during motor drive and the maincircuit unit of the inverter 7 is base-blocked, the protective diodeunits 19 and 20 secure a path for circulating current induced by motorinductance, so as to prevent the inverter 7, the winding switchingsection 2, and the winding switching section 11 from being damaged.

Even if an abnormality (e.g., motor lock) occurs during energization ofthe AC three-phase motor 1 and then the main circuit unit of theinverter 7 is base-blocked, since the protective diode units 19 and 20are provided, energy Q generated by current flowing through theinductance of the motor windings is consumed by charging an electrolyticcapacitor (not shown) in the main circuit unit of the inverter 7, thecapacitor 6, and the capacitor 15. The energy Q is expressed by Equation2 below:

Q=(½)·L·i ²   Equation 2

where L is the inductance of motor windings and i is current flowingthrough the motor windings.

An energy path will now be specifically described. Assume here that, atthe intermediate tap TU2 of the motor winding for U phase, motor currentflows in the direction from the AC three-phase motor 1 to the inverter7. In this case, circulating current flows in a closed circuit startingand ending at the intermediate tap TU2. Specifically, circulatingcurrent flows from the intermediate tap TU2, passes through a freewheeldiode in the inverter 7, charges the main circuit capacitor(electrolytic capacitor) having an impedance lower than that of thecapacitor 6, flows through the negative-side DC bus 10 and theprotective diode unit 19, and flows back to the intermediate tap TU2. Ifthe protective diode unit 19 is not present, it is not possible tosecure a path for the circulating current. Then as a result, since theenergy Q generated by current flowing through the motor winding cannotbe absorbed, the resulting rapid increase in voltage of thepositive-side DC bus 9 of the inverter 7 damages the inverter 7 and thewinding switching section 2.

To prevent such damage without the protective diode units 19 and 20, itis necessary to increase the resistance of the main circuit unit of theinverter 7 and that of the winding switching sections 2 and 11.

With the configuration described above, without increasing theresistance of the main circuit unit of the inverter 7, diode units 3 and12, and switching units 4 and 13, it is possible to provide the windingswitching apparatus capable of preventing damage caused by circulatingcurrent generated when a motor abnormality occurs.

The first embodiment discusses the case where one intermediate tap isprovided for each phase winding of the AC three-phase motor 1. The sameapplies to the cases where more than one intermediate tap is providedfor each phase winding of the AC three-phase motor 1.

For example, if two intermediate taps are provided for each phasewinding of the AC three-phase motor 1, the number of winding switchingsections is three. Likewise, for example, if three intermediate taps areprovided for each phase winding of the AC three-phase motor 1, thenumber of winding switching sections is four. In other words, the numberof winding switching sections is larger by one than that of intermediatetaps provided for each phase winding of the AC three-phase motor 1. Withthis configuration, switching of windings can be made by appropriateswitching of the winding end terminals and intermediate taps ofrespective phase windings of the AC three-phase motor 1.

FIG. 3 is a diagram illustrating a winding switching apparatus forswitching windings of an AC three-phase motor according to a secondembodiment of the present invention. Referring to FIG. 3, referencenumerals 25 and 27 denote state detectors, reference numerals 26 and 28denote comparators, reference numerals 255 and 275 denotewinding-switching-section ON-state signals, reference numerals 256 and276 denote winding-switching-section OFF-state signals, and referencenumerals 264 and 284 denote winding-switching-section abnormal signals.

The present embodiment differs from the first embodiment in that thewinding switching apparatus includes state detectors and comparators.Each state detector detects a conducting/non-conducting (cut-off) stateor an ON/OFF state of each of the power semiconductor switches includedin the switching unit of the winding switching section. Each comparatordetects an abnormality in the winding switching section on the basis ofa result of the detection made by the state detector and a drive signaloutput from the control unit of the inverter.

General operations of the state detectors and comparators will now bedescribed.

The state detector 25 detects a conducting/non-conducting state or anON/OFF state of each of the power semiconductor switches included in theswitching unit 4, and outputs the winding-switching-section ON-statesignal 255 and the winding-switching-section OFF-state signal 256 to thecomparator 26. The winding-switching-section ON-state signal 255 goeshigh when all the power semiconductor switches in the switching unit 4are in a conducting state. The winding-switching-section OFF-statesignal 256 goes low when all the power semiconductor switches in theswitching unit 4 are in a non-conducting state.

Similarly, the state detector 27 detects a conducting/non-conductingstate or an ON/OFF state of each of the power semiconductor switchesincluded in the switching unit 13, and outputs thewinding-switching-section ON-state signal 275 and thewinding-switching-section OFF-state signal 276 to the comparator 28. Thewinding-switching-section ON-state signal 275 goes high when all thepower semiconductor switches in the switching unit 13 are in aconducting state. The winding-switching-section OFF-state signal 276goes low when all the power semiconductor switches in the switching unit13 are in a non-conducting state.

The comparator 26 detects the presence or absence of an abnormality inthe winding switching section 2 on the basis of thewinding-switching-section ON-state signal 255, thewinding-switching-section OFF-state signal 256, and the drive signal 17from the control unit of the inverter 7. If an abnormality in thewinding switching section 2 is detected, the comparator 26 drives thewinding-switching-section abnormal signal 264 high and outputs it to thecontrol unit of the inverter 7.

Similarly, the comparator 28 detects the presence or absence of anabnormality in the winding switching section 11 on the basis of thewinding-switching-section ON-state signal 275, thewinding-switching-section OFF-state signal 276, and the drive signal 18from the control unit of the inverter 7. If an abnormality in thewinding switching section 11 is detected, the comparator 28 drives thewinding-switching-section abnormal signal 284 high and outputs it to thecontrol unit of the inverter 7.

The control unit of the inverter 7 inputs the winding-switching-sectionabnormal signal 264 and the winding-switching-section abnormal signal284. If at least one of the winding-switching-section abnormal signals264 and 284 is high, the control unit of the inverter 7 determines thatan abnormality has occurred, and takes an appropriate action, such ascutting off the main circuit unit of the inverter 7.

Configurations and operations of a state detector and a comparator willnow be described in detail.

FIG. 4 is a diagram illustrating detailed circuit configurations of astate detector and a comparator included in the winding switchingapparatus of the present embodiment. Specifically, the state detector 25and comparator 26 related to the winding switching section 2 areillustrated in FIG. 4. The state detector 27 and comparator 28 relatedto the winding switching section 11 will not be described here, as theyare similar to the state detector 25 and the comparator 26.

Referring to FIG. 4, reference numeral 251 denotes three photo-couplers,reference numeral 252 denotes six pull-up resistors, reference numeral253 denotes a logical negative OR (NOR) gate, reference numeral 254denotes a logical negative AND (NAND) gate, reference numerals 261 and262 denote logical exclusive OR (XOR) gates, and reference numeral 263denotes a logical OR gate.

The configuration of the state detector 25 will now be described. Thestate detector 25 includes the three photo-couplers 251, the six pull-upresistors 252, the three-input NOR gate 253, and the three-input NANDgate 254.

The anodes of light-emitting diodes of the respective threephoto-couplers 251 are connected through their corresponding pull-upresistors 252 to a gate-drive power source V_(D) for the powersemiconductor switches of the switching unit 4. The cathodes of thelight-emitting diodes of the three photo-couplers 251 are connected tothe respective collectors of the power semiconductor switches of theswitching unit 4.

The emitters of the power semiconductor switches of the switching unit 4are all connected to a gate-drive power-source ground G_(D) and thus noparticular operation is necessary here.

The emitters of photo-transistors of the respective three photo-couplers251 are all connected to a control power-source ground G_(L). Thecollectors of the photo-transistors of the three photo-couplers 251 areconnected through their corresponding pull-up resistors 252 to a controlpower source V_(L) and, at the same time, connected to theircorresponding inputs of the NOR gate 253 and NAND gate 254.

The output of the NOR gate 253 is the winding-switching-section ON-statesignal 255, and the output of the NAND gate 254 is thewinding-switching-section OFF-state signal 256.

In the present embodiment, the state detector 25 uses the photo-couplers251 to provide an insulating function. However, if the control unit andmain circuit unit of the inverter 7 and the winding switching section 2are operated at the same potential, it is not necessary that the statedetector 25 provide an insulation function.

Next, the operation of the state detector 25 will be described.

When the power semiconductor switches of the switching unit 4 are turnedon, current flows from the gate-drive power source V_(D), through thepull-up resistors 252 and the photo-couplers 251, through the powersemiconductor switches of the switching unit 4, to the gate-drivepower-source ground G_(D). This turns on the photo-transistors of thephoto-couplers 251. Since this drives all the inputs of the NOR gate 253and NAND gate 254 low, both the winding-switching-section ON-statesignal 255 (i.e., the output of the NOR gate 253) and thewinding-switching-section OFF-state signal 256 (i.e., the output of theNAND gate 254) go high.

When the power semiconductor switches of the switching unit 4 are turnedoff, no current flows through the light-emitting diodes of thephoto-couplers 251, so that the photo-transistors of the photo-couplers251 are also turned off. Since this drives all the inputs of the NORgate 253 and NAND gate 254 high, both the winding-switching-sectionON-state signal 255 (i.e., the output of the NOR gate 253) and thewinding-switching-section OFF-state signal 256 (i.e., the output of theNAND gate 254) go low.

The configuration of the comparator 26 will now be described. Thecomparator 26 includes the XOR gate 261, the XOR gate 262, and the ORgate 263.

The XOR gate 261 inputs the winding-switching-section ON-state signal255 and the drive signal 17, and outputs the XOR of the two inputsignals to the OR gate 263. The XOR gate 262 inputs thewinding-switching-section OFF-state signal 256 and the drive signal 17,and outputs the XOR of the two input signals to the OR gate 263. The ORgate 263 inputs the output signals from the XOR gate 261 and the XORgate 262. Then, the OR gate 263 outputs, as thewinding-switching-section abnormal signal 264, the OR of the two inputsignals to the control unit of the inverter 7.

Next, the operation of the comparator 26 will be described.

When all the power semiconductor switches of the switching unit 4 are ina conducting state, both the winding-switching-section ON-state signal255 and the winding-switching-section OFF-state signal 256 are high.Since the drive signal 17 is also high, the outputs of the XOR gate 261and XOR gate 262 go low, so that the winding-switching-section abnormalsignal 264 (i.e., the output of the OR gate 263) goes low.

When all the power semiconductor switches of the switching unit 4 are ina non-conducting state, both the winding-switching-section ON-statesignal 255 and the winding-switching-section OFF-state signal 256 arelow. Since the drive signal 17 is also low, the outputs of the XOR gate261 and XOR gate 262 go low, so that the winding-switching-sectionabnormal signal 264 (i.e., the output of the OR gate 263) goes low.

Thus, when the winding switching section 2 is operating properly, thewinding-switching-section abnormal signal 264 always goes low.

When the drive signal 17 is high, if not all the power semiconductorswitches of the switching unit 4 are in a conducting state, thewinding-switching-section ON-state signal 255 goes low and thewinding-switching-section OFF-state signal 256 goes high. Since thedrive signal 17 is high, the output of the XOR gate 261 goes high andthe output of the XOR gate 262 goes low, so that thewinding-switching-section abnormal signal 264 goes high.

When the drive signal 17 is low, if not all the power semiconductorswitches of the switching unit 4 are in a non-conducting state, thewinding-switching-section ON-state signal 255 goes low and thewinding-switching-section OFF-state signal 256 goes high. Since thedrive signal 17 is low, the output of the XOR gate 261 goes low and theoutput of the XOR gate 262 goes high, so that thewinding-switching-section abnormal signal 264 goes high.

Thus, whenever an abnormality is detected in the winding switchingsection 2, the winding-switching-section abnormal signal 264 goes high.

Therefore, if the winding-switching-section abnormal signal 264 goeshigh while the control unit of the inverter 7 is monitoring the state ofthe winding-switching-section abnormal signal 264, the control unit ofthe inverter 7 determines that an abnormality has occurred and can stopthe operation of the main circuit unit of the inverter 7.

In the present embodiment, each state detector detects theconducting/non-conducting state of the power semiconductor switches ofthe switching unit, and an output signal from the state detector iscompared with a drive signal that drives the switching unit. This makesit possible to detect an abnormality, such as erroneous wiring of thewinding switching section or a failure of the switching unit. It is thuspossible to provide a winding switching apparatus capable of preventingitself from being damaged.

With the embodiments described above, it is possible to realize a motordrive operation adaptable to a wide range of constant outputcharacteristics. The present invention is thus applicable to main-shaftdriving devices for machine tools and to vehicle driving devices forhybrid vehicles and electric vehicles.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

1. A winding switching apparatus comprising: a winding switching deviceconfigured to switch a plurality of windings of an AC motor which isconfigured to be driven by an inverter to supply a variable voltagehaving a variable frequency; a drive circuit configured to control thewinding switching device; and the winding switching device comprising: awinding switch configured to switch the plurality of windings based on awinding-switching signal from the drive circuit; a diode bridgeincluding a positive-side DC output terminal, a negative-side DC outputterminal, and AC input terminals, the AC input terminals correspondingto respective phases of the AC motor, the positive-side andnegative-side DC output terminals being respectively connected topositive-side and negative-side DC buses provided in the inverter, theAC input terminals being respectively connected to winding-switchingterminals corresponding to the respective phases of the AC motor, the ACinput terminals being respectively connected to phase terminals providedin the winding switch; and a capacitor connecting the positive-side DCoutput terminal to the negative-side DC output terminal.
 2. The windingswitching apparatus according to claim 1, wherein the winding switchincludes power semiconductor switches and diodes, the powersemiconductor switches corresponding to the respective phases, thediodes being connected in inverse parallel to the respective powersemiconductor switches, emitters of the respective power semiconductorswitches are connected to each other, and collectors of the respectivepower semiconductor switches are respectively connected to the AC inputterminals of the diode bridge.
 3. The winding switching apparatusaccording to claim 2, wherein the diode bridge includes a diode deviceand a protective diode device, the diode device includes diodescorresponding to the respective phases, cathodes provided in therespective diodes of the diode device being connected to each other, andthe protective diode device includes diodes corresponding to therespective phases, anodes provided in the respective diodes of theprotective diode device being connected to each other, cathodes providedin the respective diodes of the protective diode device beingrespectively connected to the cathodes provided in the respective diodesof the diode device.
 4. The winding switching apparatus according toclaim 2, wherein the winding switching device includes a positive-sidecharging resistor and a negative-side charging resistor, thepositive-side charging resistor includes a first end and a second end,the first end of the positive-side charging resistor being connected tothe positive-side DC bus provided in the inverter, the second end of thepositive-side charging resistor being connected to a positive side ofthe capacitor, and the negative-side charging resistor including a firstend and a second end, the first end of the negative-side chargingresistor being connected to the negative-side DC bus provided in theinverter, the second end of the negative-side charging resistor beingconnected to a negative side of the capacitor.
 5. The winding switchingapparatus according to claim 2, further comprising: a plurality of statedetectors each configured to detect a conducting state of the powersemiconductor switches of the corresponding switching device; and aplurality of comparators each configured to detect an abnormality in thecorresponding winding switching device on the basis of output signalsfrom the corresponding state detector and a drive signal.
 6. The windingswitching apparatus according to claim 5, wherein the state detector isconfigured to detect that all the power semiconductor switches are in aconducting state or that all the power semiconductor switches are in anon-conducting state.
 7. The winding switching apparatus according toclaim 5, wherein the state detector has an insulating function.
 8. Thewinding switching apparatus according to claim 5, wherein the comparatorincludes a plurality of logical exclusive OR circuits each configured tocompare an output signal from the corresponding state detector with thedrive signal to output a logical exclusive OR signal, and is configuredto use the logical exclusive OR signals from the logical exclusive ORcircuits to detect an abnormality in the corresponding winding switchingdevice.
 9. The winding switching apparatus according to claim 1, whereinthe diode bridge includes a diode device and a protective diode device,the diode device includes diodes corresponding to the respective phases,cathodes provided in the respective diodes of the diode device beingconnected to each other, and the protective diode device includes diodescorresponding to the respective phases, anodes provided in therespective diodes of the protective diode device being connected to eachother, cathodes provided in the respective diodes of the protectivediode device being respectively connected to the cathodes provided inthe respective diodes of the diode device.
 10. The winding switchingapparatus according to claim 1, wherein the winding switching deviceincludes a positive-side charging resistor and a negative-side chargingresistor, the positive-side charging resistor includes a first end and asecond end, the first end of the positive-side charging resistor beingconnected to the positive-side DC bus provided in the inverter, thesecond end of the positive-side charging resistor being connected to apositive side of the capacitor, and the negative-side charging resistorincluding a first end and a second end, the first end of thenegative-side charging resistor being connected to the negative-side DCbus provided in the inverter, the second end of the negative-sidecharging resistor being connected to a negative side of the capacitor.11. The winding switching apparatus according to claim 1, furthercomprising: a plurality of state detectors each configured to detect aconducting state of the power semiconductor switches of thecorresponding winding switch; and a plurality of comparators eachconfigured to detect an abnormality in the corresponding windingswitching device on the basis of output signals from the correspondingstate detector and a drive signal.
 12. The winding switching apparatusaccording to claim 11, wherein the state detector is configured todetect that all the power semiconductor switches are in a conductingstate or that all the power semiconductor switches are in anon-conducting state.
 13. The winding switching apparatus according toclaim 11, wherein the state detector has an insulating function.
 14. Thewinding switching apparatus according to claim 11, wherein thecomparator includes a plurality of logical exclusive OR circuits eachconfigured to compare an output signal from the corresponding statedetector with the drive signal to output a logical exclusive OR signal,and is configured to use the logical exclusive OR signals from thelogical exclusive OR circuits to detect an abnormality in thecorresponding winding switching device.
 15. A winding switching systemcomprising: an AC motor; an inverter to supply a variable voltage havinga variable frequency; a winding switching device configured to switch aplurality of windings of the AC motor which is configured to be drivenby the inverter; a drive circuit configured to control the windingswitching device; and the winding switching device comprising: a windingswitch configured to switch the plurality of windings based on awinding-switching signal from the drive circuit; a diode bridgeincluding a positive-side DC output terminal, a negative-side DC outputterminal, and AC input terminals, the AC input terminals correspondingto respective phases of the AC motor, the positive-side andnegative-side DC output terminals being respectively connected topositive-side and negative-side DC buses provided in the inverter, theAC input terminals being respectively connected to winding-switchingterminals corresponding to the respective phases of the AC motor, the ACinput terminals being respectively connected to phase terminals providedin the winding switch; and a capacitor connecting the positive-side DCoutput terminal to the negative-side DC output terminal.
 16. The windingswitching system according to claim 15, wherein the winding switchincludes power semiconductor switches and diodes, the powersemiconductor switches corresponding to the respective phases, thediodes being connected in inverse parallel to the respective powersemiconductor switches, emitters of the respective power semiconductorswitches are connected to each other, and collectors of the respectivepower semiconductor switches are respectively connected to the AC inputterminals of the diode bridge.
 17. The winding switching systemaccording to claim 15, wherein the diode bridge includes a diode deviceand a protective diode device, the diode device includes diodescorresponding to the respective phases, cathodes provided in therespective diodes of the diode device being connected to each other, andthe protective diode device includes diodes corresponding to therespective phases, anodes provided in the respective diodes of theprotective diode device being connected to each other, cathodes providedin the respective diodes of the protective diode device beingrespectively connected to the cathodes provided in the respective diodesof the diode device.
 18. The winding switching system according to claim15, wherein the winding switching device includes a positive-sidecharging resistor and a negative-side charging resistor, thepositive-side charging resistor includes a first end and a second end,the first end of the positive-side charging resistor being connected tothe positive-side DC bus provided in the inverter, the second end of thepositive-side charging resistor being connected to a positive side ofthe capacitor, and the negative-side charging resistor including a firstend and a second end, the first end of the negative-side chargingresistor being connected to the negative-side DC bus provided in theinverter, the second end of the negative-side charging resistor beingconnected to a negative side of the capacitor.
 19. The winding switchingsystem according to claim 15, further comprising: a plurality of statedetectors each configured to detect a conducting state of the powersemiconductor switches of the corresponding winding switch; and aplurality of comparators each configured to detect an abnormality in thecorresponding winding switching device on the basis of output signalsfrom the corresponding state detector and a drive signal.
 20. Thewinding switching system according to claim 19, wherein the statedetector is configured to detect that all the power semiconductorswitches are in a conducting state or that all the power semiconductorswitches are in a non-conducting state.